Low watts & low HR: nutrition or lack of endurance?

Hi everyone,

Just concluded a 135km race with approx 3.6k meters of elevation gain.

I was doing fine until the last 2-3kms on the last climb when in that moment I faded to the point I could no longer push decent watts (I was doing mid z2 at best) and my hr was also relatively contained in high z2 / low z3

I’m curious as to how I should interpret this: did I not fuel enough for that final climb or it is a general sign of lack of endurance when watts and hr almost align but cannot push power?

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Sounds like a clear sign of being glycogen depleted to me. Not being to able to get HR or power up are both ways in which the body limits your output to conserve energy for brain function etc. In addition, the fact that you had already ridden 130km with that much climbing suggests that a bonking scenario would not be unlikely unless you were obsessively on top of eating from the start.


It could be a combination, what was your nutrition that morning and during the ride?

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I’d add “and did you do any training rides of that distance or with similar elevation”

Breakfast was indeed light as it was an early start.

So I was relying on glycogen reserves and furling during the ride.

Tbh I thought I was carrying enough but it probably wasn’t the case.

Yes, one which was exactly the same a few weeks back (in a more fatigued state though) plus several long endurance rides since the beginning of the year.

OT: Unlike past seasons though I have focused less on tempo training based on the fact that many seemed to suggest that it’s not important to match the duration of the target event etc.
I was a bit sceptical but I think, as you alluded, that I should try to replicate the demands of the event also in training more often and focus on z3 again.

Back on topic, my doubt then was whether a lack of endurance manifests itself in a significant cardiac drift which is unlike what happened in this case when both power and hr were depressed which might be explained by glycogen depletion as Calle was suggesting.

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I have a tendency to over fuel during an event. If that’s even possible. So can’t help there. But I am better if I train longer distances at a higher than Z2 level. Sounds like 100mg of caffeine 30 min before that climb would have helped.

Classic signs of glycogen depletion.

Big mistake.
In the past when I had an early race start (think 7 am), my team and would get up at 3:30 or so and start by eating something. That isn’t pleasant and why early starts are not my favorite. But adrenaline takes care of the lack of sleep. How I have slept the two nights before made a difference, too.

What also matters big time is what you have eaten the day before. A big bowl of pasta is a good way to prep.

What did your nutrition look like? How many gels and chews did you ingest in total? How many g of carbs per hour did you take in? How much did you drink?

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I had planned a flask with 300g of table sugar and 200g in gels.

I say planned because I dropped the flask just before the start and at least 50g spilled out :sweat:

I consumed all the gels with no problem but I’m also wondering whether it might be worthwhile to “load” and empty the flask during the first hours of the event as it seems easier than during the final stages.
In fact, I still had something left at the end of the event.

Hey @jz91! Yeah, it sounds to me like you bonked.

I had the same experience in my first year at Lost And Found, a similar effort to your race. 100 miles with about 10,000 feet of climbing.

I was feeling super strong until I came on to the last climb and started feeling tired until seeing tunnel vision when almost to the top. Had it not been for a fellow rider who I’d been riding with back and forth, I don’t think I would have finished. I pedaled embarrassingly slow on our final descent to the finish line; I was too proud to have him push me :sweat_smile:.

I personally didn’t lack fitness for the event since I knew I was well trained; instead, I realized I was very under-fulled because as soon as I had something to eat and drink, I felt like myself again. The following year I took a different approach to fuel during the race, making sure I was feeding my body energy at a consistent rate so I wouldn’t bonk, and I finished with really good energy and enough leg power to crank it up to the finish line.

I am not sure what fueling strategy you used but here is a good article on the subject and how important fueling is: What is Bonking? Causes, Dangers, and Prevention - TrainerRoad Blog


Thanks for the input!!

Ahha yeah I definitely had tunnel vision as well.
I stopped at the top of the climb at the feeding station to get a coke and when I started descending I wasn’t entirely lucid :see_no_evil:

Would you think it make sense to “front-load” the fueling perhaps during the first half of the race when it feels the body is able to better absorb it? Clearly I’d keep eating through the final stages but I was wondering whether this might be a good strategy.


The general consensus until recently seemed to hover around 90g of carbs (60g glucose and 30g of fructose) an hour during a race, but apparently you can take in more fructose than that so instead of 2:1 you can do 1:0.8 for a total of 108g. I prefer 2:1 because the fructose makes my drink seem a lot sweeter and I find it less appealing. Ideally you would practice that beforehand so you would know if it causes any stomach trouble for you. Doing more than that could cause issues, even if the issue is just a sloshy stomach. If you try to preload by dramatically exceeding that I think you are going to start having trouble, especially over three hours.


I grabbed a Coke as well!

As the article I shared says: “Each of us have our own unique carbohydrate and caloric intake requirement, and individual tolerance for what we can stomach during a workout or race.” So you have to see what works for you.

Normally I would make sure I’d start hydrating at least a week before the event because it takes time for the body to be properly hydrated.

Then on race day, I would have a normal breakfast a few hours before the start time. Then for this ride in specific, I remember I tried the following, and it worked for me:

1 bottle of water only
1 bottle of water + electrolytes
1 gel every 40 minutes
2 capsules of Sportslegs every 2 hours

This seemed to do the trick for me. I would get water at each aid station and not intake any other random kind of food provided as I did the year prior.

Disclosure: This worked for me; you may need a different approach depending on how you know your body works. There are other pro athletes taking in as much as 160g/hr through drink mix and gels only, so your specific milage may vary!

Normally, if you tend to do long endurance training rides, you can test things there and bring them on to race day, so you are not trying anything new that day! You train like you would race. However, the only thing that I personally swap out are gels for figs :face_with_open_eyes_and_hand_over_mouth:. I wouldn’t be able to stomach that much gel in my life haha.